This invention relates to a method and system for controlling flatness in sheet metal by detecting the variation in the roll crown.
Recently, there has arisen an increasingly demand for the accuracy in the thickness of a cold rolled strip. With the development of an automatic gauge control means (AGC), a satisfactory uniformity in gauge of a strip can be attained in the rolling direction. However, no satisfactory control method has been realized for achieving an accuracy in gauge of a strip in the widthwise direction and, especially, the flatness of the strip. A known method for controlling the flatness of a strip (or shape control) is a roll bending method, wherein the variation in the roll crown due to wear and/or thermal expansion (heat crown) of rolls (the latter is caused by the heat radiation from the strip being rolled as well as by the heat caused by the deformation of a strip) must be compensated for to control the flatness of a strip. This control method, however, is no longer employed widely, because difficulties are encountered in determining the extent of the roll crown varied due to wear and heat and therefore a roll bending force cannot be set beforehand.